Asymmetric Design: A Way for Optimizing Electric Motor’s Performance

By Farnam Farshbaf | 07/11/2022

Introduction 

The invention of electric motors (E-motors) has drastically transformed and revolutionized every aspect of our daily lives. The ever-growing demand for E-motors has expanded to cover a wide range of applications such as home appliances, medical devices, robotic arms, space shuttles, etc. Moreover, the environmental crises alongside the increasing price of fuel gases have accelerated the transition of the global market to the Electric Vehicle (EV) industry. 

The figure below shows the increasing global sales of EVs from 2012 to 2021 hence, demonstrating the importance of the EV industry in coming years. 


Global Sales of EVs in Recent Years [1] 


Given the fact that the performance of the E-motor plays a crucial role in determining the efficiency and capability of the propulsion system of the EV, a considerable amount of recent research has been conducted to effectively improve and ultimately optimize the E-motor’s structure. Both academia and industry are working collaboratively to achieve this goal and eventually provide a sustainable solution for the transportation system. To help the engineers and researchers in their endeavors, EMWorks has dedicated a comprehensive package for E-motors analysis; making it possible to design and analyze a plethora of topologies and achieve the optimal solutions for EV and other applications. 


 E-Motor Design using MotorWizard Tool


This article presents a technical summary of one the novel design methods called “Asymmetric Design” to deliver a better performance of E-motors such as higher power density, lower torque ripple, and an optimal utilization of materials like permanent magnets. For this purpose, we will start by defining the concept of “asymmetric design” and how a motor can be asymmetric in terms of shape and structure. Next, we will dive into the analysis and comparison of the E-motor’s performance before and after applying asymmetricity through the design procedure and show how the asymmetric design improves the performance of the machine from an electromagnetic perspective. We will conclude with a summary of the findings of present work as well as some potential venues for future research.  

Definition of Asymmetric Design 

The general design procedure of E-motors consists of several steps. Different design parameters such as inner and outer diameter, the width and height of stator teeth, and magnet dimensions must be determined for the initial design. After that, through an iterative calculation process, the design parameters change to reach an optimum design matching with design requirements. The figure below illustrates the main aspects of the design and optimization of E-motors in one frame. 


 Main Aspects for the Design and Optimization of E-Motors [2] 


According to this figure, choosing a proper motor type and its topology is a crucial step toward achieving the best possible design based on pre-defined constraints. Adopting an “Asymmetric” shape for the E-motor design can occur at this very first step. The figures (a) and (b) compare the differences between two interior permanent magnet synchronous motors (IPMSMs) as an example of symmetric and asymmetric designs. 


IPMSM Cross-Section with (a) Asymmetric Design (b) Symmetric Design [3] 


As shown in the symmetric and conventional design, the magnets and the barriers follow a symmetric pattern. However, the presence of additional flux barriers in the asymmetric design caused asymmetry in the cross-section leading to new design capabilities. Induction motor (IM) with an axially skewed structure is a well-known example of asymmetric E-motor designs.   


Construction of an IM’s Squirrel Cage Rotor with a Skew Structure [4] 


Moreover, the growing interest in PM-based motors due to their distinguished performance has attracted researchers to explore new venues to implement asymmetric design approaches in PM-based machines. The figure below exhibits a recent categorization of IPMSMs based on different asymmetric design methods.